Thermoplastic plastics films, such as polyvinyl chloride films are often produced on so-called "F-calenders". An "F-calenders" comprises three calendering rollers disposed vertically above one another in a support column and a fourth calendering roller disposed in the same horizontal plane as the uppermost roller of the set of three rollers. This fourth roller may be either in front of or behind the uppermost roller.
The strand-like polyvinyl chloride material to be processed into a film is fed into the nip between the two rollers disposed adjacent one another in the same horizontal plane. The material passes through the nips between the three rollers disposed vertically above one another. The film which is produced thus loops around at least a portion of each roller.
From the lowermost roller of the F-calender, the film--is collected by a take-up roller train, comprising a plurality of take-up rollers. In the take-up roller train, the film is stretched to up to twice its original dimension.
The take-up rollers are each individually driven and heated by means of a circulating medium, such as water or oil. The take-up rollers generally have a diameter of between 150 and 200 mm and a length of between 2,200 and 2,600 mm, the actual dimensions depending upon the working width of the calender rollers. Because of their weight and dimensions, such take-up rollers can only be removed by a lifting mechanism. This removal is necessary when it is desirable, for example, to employ rollers with a different surface, that is to say, having a different peak-to-valley height, or when the heads of the circulation system for the temperature-controlling medium start leaking, or when bearings become damaged.
Individual take-up rollers are very difficult to replace and the process is extremely time-consuming. This is because, especially in the case of an F-calender, it has hitherto been impossible to use a lifting mechanism in view of the fact that the fourth roller, including its bearing and its adjustment means, is disposed vertically above the take-up roller train. In consequence, the take-up roller cannot be raised and removed in an upward direction.
Hitherto, therefore, the removal of an individual take-up roller has been effected by slightly raising both ends of the roller at its journals by means of lifting trucks or the like. The drive coupling rod at one end of the roller journal and the snap coupling for the circulating temperature-controlling medium at the other end are then released. It is then necessary for a long guide and support bar to be slipped beneath the appropriate take-up roller, so that the roller can be withdrawn laterally from the region of the calender support columns on such bar. Such a removal process means that the entire calender line is out of action for a relatively long time. Moreover, damage may be caused to the extremely delicate shell of the take-up roller.
An L-calender is disclosed in U.S. Pat. No. 3,581,340. This calender includes a take-up roller train disposed on the final calender roller when viewed in the operating direction. In such an arrangement, the take-up roller train and the embossing means are disposed on a displaceable truck. However, such prior document does not disclose any means for removing individual take-up rollers from the calender support columns, and it must therefore be assumed that the removal process described hereinbefore still has to be effected.
An F-calender is also described in German Pat. Specification No. 3 506 256. Such calender also has a take-up roller train disposed after the final calender roller, when viewed in the operating direction. A displaceable and pivotable embossing means is disposed downstream of the take-up roller train when viewed in the operating direction. Again, however, no means for removing individual take-up rollers from the take-up roller train are disclosed in this prior publication.